The long-term goals of this project are to identify and elucidate the physiological and pathophysiological signaling mechanisms involved in the regulation of pulmonary vascular function mediated by modulation of cGMP generation by poorly understood processes that control the soluble form of guanylate cyclase (sGC). Our studies focus on integrating our understanding in isolated bovine pulmonary arteries of how heme metabolism and various redox-related processes interact with the metabolism of reactive oxygen species (ROS) and nitric oxide (NO) in the control of pulmonary arterial smooth muscle force through mechanisms involving the regulation of sGC. Aim 1 investigates defining how the modulation of specific pathways regulating Nox oxidases by mediators promoting pulmonary hypertension (PH) control pulmonary arterial smooth muscle force through ROS mechanisms that regulate the activity of sGC. Studies in Aim 2 examine how cytosolic NADH, NADPH and glutathione redox regulate sGC through modulating oxidation of its thiol and heme sites, with an emphasis on identifying how these mechanisms of sGC regulation contribute to the actions of PH mediators and inhibit vascular responses involving nitric oxide (NO) and ROS. Aim 3 studies examine how the control of heme biosynthesis by aminolevulinic acid (ALA) generating protoporphyrin IX, and heme metabolism by heme oxygenase (HO) regulate the activity of sGC and its control of pulmonary vascular force by cGMP. Endothelium-removed bovine pulmonary arteries are studied with a combination of physiological function, molecular signaling, organ culture, transfection and metabolic modulation approaches to investigate mechanisms controlling sGC and its influence on vascular force through cGMP. Arteries from mice deficient in Nox-2 and p47phox Nox oxidase subunits, glucose-6-phopshate dehydrogenase needed to maintain cytosolic NADPH, and HO-2 are used to support mechanistic studies by defining their role in regulating sGC. Pulmonary arteries from monocrotaline-induced PH rats are examined to identify alterations in the regulation of sGC by the Nox oxidase, ROS and redox systems investigated. The regulation of sGC by ALA-elicited protoporphyrin IX generation is examined in a manner that determines if it stimulates sGC in a manner that has potential for therapeutic development as a pulmonary vasodilator which is resistant to oxidant conditions that are likely to be inhibiting sGC in PH.